The eggshell of Drosophila melanogaster is composed of three layers whose synthesis and assembly is sequentially carried out by the follicular epithelium as each egg chamber attains the appropriate developmental stage. Since many different proteins are involved, eggshell production requires a mechanism to temporally coordinate the sequential synthesis. It is the nature of this developmental control mechanism that we want to ultimately illucidate. The present grant represents a first phase towards this goal; that is, to chromosomally map the major genes involved in the eggshell production. We proposed to accomplish this using two approaches: (1) by searching for electrophoretic variants in natural populations of Drosophila melanogaster and then genetically mapping the source of these variations; and (2) by carefully screening already existing female sterile mutation for those whose primary defects are in eggshell structures and then, if not already known, determining the location of the mutation and characterizing the detailed structural and biochemical nature of the shell defect.